1. Field of the Invention
The present invention is directed to a structure for attaching a seat back to the body of a vehicle, and more specifically to a structure to attach the rear seat back to the floor of a car body.
2. Description of Related Art
Vehicle seats, for example car seats, must have enough structural strength and rigidity to withstand the reaction and impact forces arising in an accident due to the mass of a seated passenger. These forces must also be considered when designing attachments of the seat to a vehicle.
FIG. 8 shows as an example a perspective view of a rear seat's surroundings within the vehicle cabin. The rear seat (100) in FIG. 8 has a seat back (101) that is divided in two along the length of the vehicle. When the seat back (101) is folded forward, the vehicle cabin and the trunk are connected and form one integral empty space. When rear seat back (101) is upright, the trunk space to store cargo is located behind the rear seats (100).
When a car of this type sustains a frontal impact, cargo in the trunk space moves forward owing to its inertia. Thus, the weight of that cargo acts directly on the seat backs as an impact force. It is necessary for the seat backs (101) to have sufficient strength to withstand that impact as well as forces due to the seated passengers, therefore the seats must be attached to the vehicle body with sufficiently strong attachment structures. These requirements of high structural strength also exist with respect to seat belts attachment points.
One example of a conventional seat back (101) attachment structure is shown in FIGS. 9a and 9b, depicting a cross section taken along line A--A of FIG. 8, which extends front-to-back in the vehicle at the location where the seat backs (101) are divided. FIGS. 9a and 9b show two different conventional attachment structures, where the seat backs (101) and cushions (102) are depicted as broken lines.
In FIG. 9a a seat back (101) is joined to a center hinge (103) near the bottom of the seat backs where the seats are divided. Center hinge (103) is attached to the rear floor panel (104) by threaded fasteners, and a reinforcement plate (105) is used as a backing. In FIG. 9b, the hinge (103) is attached to a bracket (106) welded firmly to the rear floor panel (104). In these designs, any impact force exerted on seat back (101) is transferred from the center hinge (103) to the rear floor panel (104). Ultimately, the rear floor panel (104) absorbs this impact force, and it becomes difficult to further improve rigidity and strength of the structure.
The center hinge (103) is mounted to the rear floor panel (104) as a single unit, and is a large item. Thus, it is difficult to position the center hinge in the correct alignment during assembly. Correctly positioning these parts requires many man hours, resulting in reduced manufacturing efficiency. Even if a setting jig is used, the setting position of the center hinge is essentially in the center of the rear floor panel, and so the setting jig itself also has to be large-sized to reach that position.